Carbon-containing lithium-iron composite phosphorus oxide for lithium secondary battery positive electrode active material and process for producing the same

Abstract

A carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material, includes particles being composed of a lithium-iron composite phosphorus oxide having an olivine structure whose basic composition is LiFePO 4 , and being composited with carbonaceous fine particles. A process for producing the same includes the steps of mixing a lithium compound making a lithium source, an iron compound making an iron source, a phosphorus-containing ammonium salt making a phosphorus source and carbonaceous fine particles, thereby preparing a mixture, and calcicing the mixture at a temperature of from 600° C. or more to 750° C. or less.

1. A carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material, comprising particles being composed of a lithium-iron composite phosphorus oxide having an olivine structure whose basic composition is LiFePO 4,  and being composited with carbonaceous fine particles, wherein a molar ratio of carbon atoms in said carbonaceous fine particles with respect to lithium atoms falls in a range of from 0.02 or more to 0.2 or less, and wherein said carbonaceous fine particles have an average particle diameter of from 5 nm or more to 100 nm or less. 
     
     
       2. The carbon-containing lithium-iron composite phosphorous oxide for a lithium secondary battery positive electrode active material according to  claim 1 , wherein said carbonaceous fine particles comprise carbon black. 
     
     
       3. The carbon-containing lithium-iron composite phosphorous oxide for a lithium secondary battery positive electrode active material according to  claim 1 , wherein the carbon-containing lithium-iron composite phosphorous oxide is formed as particles having an average particle diameter of from 0.2 μm or more to 5 μm or less. 
     
     
       4. The carbon-containing lithium-iron composite phosphorous oxide for a lithium secondary battery positive electrode active material according to  claim 1 , wherein said lithium-iron composite phosphorus oxide is expressed by a composition formula, LiFe 1-x M x PO 4 , wherein “M” is at least one element selected from the group consisting of Mn, Mg, Ni, Co, Cu, Zn and Ge and a substitution proportion “x” is 0.02≦“x”≦0.2. 
     
     
       5. The carbon-containing lithium-iron composite phosphorous oxide for a lithium secondary battery positive electrode active material according to  claim 4 , wherein the element “M” in said composition formula is Mn. 
     
     
       6. The carbon-containing lithium-iron composite phosphorous oxide for a lithium secondary battery positive electrode active material according to  claim 4 , wherein the substitution proportion “x” of the element “M” in said composition formula is 0.05 ≦“x”≦0.15. 
     
     
       7. A process for producing a carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material, in which particles being composed of a lithium-iron composite phosphorus oxide having an olivine structure whose basic composition is LiFePO 4 , are composited with carbonaceous fine particles, the process comprising the steps of:
 mixing a lithium compound making a lithium source, an iron compound making an iron source, a phosphorus-containing ammonium salt making a phosphorus source and carbonaceous fine particles, wherein a molar ratio of carbon atoms in said carbonaceous fine particles with respect to lithium atoms falls in a range of from 0.02 or more to 0.2 or less, and wherein said carbonaceous fine particles have an average particle diameter of from 5 nm or more to 100 nm or less, thereby preparing a mixture; and 
 calcining the mixture at a temperature of from 600° C. or more to 750° C. or less. 
 
     
     
       8. The process for producing a carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material according to  claim 7 , wherein Li 2 CO 3  making said lithium source, FeC 2 O 4 ·2H 2 O making said iron source, NH 4 H 2 PO 4  making said phosphorus source and carbon black being said carbonaceous fine particles are mixed in said mixing step. 
     
     
       9. The process for producing a carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material according to  claim 7 , wherein LiH 2 PO 4  making said lithium source as well as said phosphorus source, FeC 2 O 4 ·2H 2 O making said iron source and carbon black being said carbonaceous fine particles are mixed in said mixing step. 
     
     
       10. The process for producing a carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material according to  claim 7 , wherein the calcining temperature falls in a range of from 620° C. or more to 700° C. or less in said calcining step. 
     
     
       11. The process for producing a carbon-containing lithium-iron composite phosphorus oxide for a lithium secondary battery positive electrode active material according to  claim 7 , wherein said calcining step is carried out in an inert or in a reducing atmosphere. 
     
     
       12. A lithium secondary battery, comprising a positive electrode including the carbon-containing lithium-iron composite phosphorus oxide according to  claim 1 .